This invention relates to novel synergistic stabilizer compositions comprising an organotin halide borate and an organic thiol compound. Additionally, this invention relates to methods for improving the resistance to early color formation during processing of vinyl halide homopolymers, copolymers and mixtures of polymers containing vinyl halide homopolymers or copolymers. Further, this invention relates to plastic compositions comprising (1) vinyl halide homopolymers or copolymers or mixture of polymers containing vinyl halide homopolymer or copolymer, and (2) a synergistic stabilizer composition comprising an organotin halide borate and an organic thiol.
It is well known in the plastic art to process organic polymeric materials, particularly thermoplastic materials, at elevated temperatures into intermediate and finished products of commerce. Such processes as injection molding, extrusion, roll milling and blowing are conventionally employed to produce useful thermoplastic products such as pipes, bottles, baskets, etc. Vinyl halide polymers (e.g., polyvinyl chloride), copolymers and mixtures of polymers which contain vinyl halide polymers or copolymers are conveniently processed by these well known art methods. However, during the elevated temperature processing of plastics, particularly the thermoplastics, more particularly the vinyl halide homopolymers, vinyl halide copolymers and mixtures of polymers which contain vinyl halide homopolymers or vinyl halide copolymers degradation of the plastic often occurs. This degradation is manifested by undesirable changes in physical properties, changes in processing behavior and often a development or change of color and is particularly noticeable in unstabilized plastics (i.e., plastics which do not contain stabilizers). Degradation or discoloration during processing is particularly undesirable in clear or lightly colored plastics. Therefore, it is desirable to prevent or inhibit such undesirable changes and the discoloration of plastics druing processing so as to achieve useful products free of discoloration.
To inhibit or prevent discoloration of vinyl halide homopolymers, vinyl halide copolymers and mixtures of polymers containing vinyl halide homopolymers or vinyl halide copolymers it has been known in the art to incorporate therein such materials as organic thiols, hindered phenols, tin carboxylates, organotin carboxylates, and organotin mercaptides. Synergistic combinations such as a combination of an organic thioanhydride and a monohydrocarbyl tin compound having the formula R.sup.3 Sn(Z).sub.n (Z'R.sup.4).sub.3.sub.-2n where R.sup.3 is a 1 to 12 carbon atom hydrocarbyl radical, Z and Z' are either oxygen or sulfur, R.sup.4 is hydrogen or an organic radical bonded to Z' by a carbon atom and n is 0-1.5 as disclosed in U.S. Pat. No. 3,822,233, have also been reported for improving the resistance of halogen containing resin to early color development during processing. Organotin compounds of the general formula (R.sub.2 Sn).sub.3.sub.-n (R.sup.1).sub.2n (BO.sub.3).sub.2 where R and R.sup.1 are univalent organic radicals selected from the class consisting of alkyl, aryl, and aralkyl radicals and n is 0,1 or 2 are disclosed as stabilizers for chlorine containing polymers (e.g. polyvinyl chloride) by H. E. Ramsden in U.S. Pat. No. 2,867,641. Ramsden described these compounds as organotin borates or their partially esterified products. It is pointed out by the inventors that the compounds disclosed by Ramsden are particularly free of ##STR1## cyclic structures where n is 0 or 1, (2) tin-oxygen-tin bonding and (3) tin-halogen bonding of the organotin compounds of the stabilizer compositions of this invention. Many of these materials which have been used or suggested to be used to improve the resistance of halogen containing resins to early color development during processing have not been entirely satisfactory, or are expensive or are difficult to make, or have undesirable properties such as being odoriferous during processing of the plastic or in themselves impart some initial color to the plastic. The combination of an organotin borate with an organic thiol as a stabilizer composition has been disclosed in U.S. Pat. No. 3,928,285 issued Dec. 23, 1975 to the same inventors as in this invention. However, the organotin borates of the stabilizer compositions of U.S. Pat. No. 3,928,285 do not contain the tin-halogen bond of the organotin borates of this invention. That organotin borates having a tin-halogen bond form in synergistic combination with an organic thiol stabilizer compositions to stabilize vinyl halide homopolymer or copolymers or polymer mixtures containing vinyl halide hompolymers or copolymers is only taught to the art by this invention.
Organotin borate compounds heretofore known in the art for use in stabilizing polymers are in many instances known to exhibit significant hydrolytic instability. However, in contrast to many of the prior art organotin borate stabilizers the organotin halide borate compounds of the stabilizer compositions of this invention exhibit good resistance to hydrolysis.
It is, therefore, an object of this invention to provide a synergistic stabilizer composition comprising an organotin halide borate and an organic thiol compound for improving the resistance of halogen containing polymers to early color development during processing at elevated temperatures. A further object of this invention is to provide a plastic composition exhibiting improved resistance to early color development during elevated temperature processing. A still further object of this invention is to provide a method for improving the resistance to early color formation of halogen containing polymers.